1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus using a process cartridge, and more particularly to an image forming apparatus using a process cartridge capable of accurately and easily coupling a drive shaft and a developing roller without preventing easy installation of the process cartridge in the image forming apparatus.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile capabilities typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet of recording media; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
In such image forming apparatuses, the developing device and the photoconductor are often formed together as a single integrated unit to construct a process cartridge detachably installable in the image forming apparatuses.
However, even with such a process cartridge, a drive source for the photoconductor and the developing device both installed in the process cartridge is provided to a main body of the image forming apparatus. Therefore, it is important to accurately install the process cartridge in the image forming apparatus in order to prevent uneven image density or banding in resultant images stemming from defective coupling.
There is known a mechanism that accurately couples a drive shaft of a drive source provided to a main body of an image forming apparatus to a driven shaft provided to a process cartridge.
In one example of an image forming apparatus incorporating such a mechanism, a drive shaft provided to a main body of an image forming apparatus is supported by first and second bearings. The second bearing functions as a tentative holding member having a degree of freedom in a radial direction to absorb displacement between the drive shaft and a driven shaft of the developing device provided to the process cartridge. Although generally successful for its intended purpose, with such a configuration there is a risk that a coupling that couples the drive shaft and the driven shaft may slip, causing uneven image density or banding in resultant images.
In another approach, in addition to provide the second bearing as the tentative holding member as described above, a constant-velocity joint is used as the coupling that couples the drive shaft and the driven shaft. However, use of the tentative holding member and the constant-velocity joint, although successful for its intended purpose, increases production costs and complicates assembly.